A satellite utilizes a hub and spoke routing model, where the satellite is located at the hub and “surrounding” ground terminals are in communication with the satellite (hub) via links or spokes. Rather than viewing each spoke or link as a bi-directional link, each spoke may instead be viewed as a pair of asymmetrical, unidirectional links. In satellite environments bandwidth is an extremely precious commodity, making fine-grain control desirable. Since the hub has little control over the use of bandwidth on the upstream links (i.e., from respective ground terminals to the satellite), bandwidth conservation of this mechanism is focused on downstream links.
Fine-grain control is facilitated by providing individual descriptors, classifying, buffering, queuing and scheduling capabilities and resources for each downstream link. This works well for unicast traffic, but it can lead to sub-optimum bandwidth usage for downstream multicast traffic. Upstream traffic, i.e., in the spoke-to-hub direction, is not a candidate for optimization because spokes can only communicate with the hub, i.e., communication is point-to-point. This communication path is referred to as the “uplink.” The hub has broadcast capabilities to all spokes from which bandwidth can be reclaimed. The hub-to-spoke direction is referred to as the “downlink.”